We propose to advance chromosome biology and cytogenetic research by developing a scanning flow cytometer that measures both the total amount and distribution of fluorescent DNA stain along chromosomes, and by incorporating these measurement techniques into a flow sorter to purify chromosomes of a single type. Two scanning techniques, single-slit-scanning and fringe scanning, will be used to measure chromosome profiles. In both techniques, fluorescently stained chromosomes are forced to flow lengthwise one-at-a-time through a measurement region. In the single slit approach, the chromosomes are scanned as they cross a single 1 micron thick ribbon of laser light; while in the fringe approach, the chromosomes are scanned as they cross several parallel regions of intense illumination (interference fringes) spaced about 0.4 microns apart, produced by intersecting laser beams. Both single-slit-scanning and fringe scanning techniques will allow measurement of total DNA fluorescence to within two percent while measuring chromosomes at rates up to 2 x 10 to 4th power per second. The single slit approach will allow measurement of centromeric index for the longer human chromosomes. Fringe scanning will allow higher resolution measurement (approaching that found in the light microscope) and may even allow measurement of chromosome bands. Single-slit scanning (technically straightforward) will be installed on an ultra-high-speed flow sorter to allow increased chromosome resolution and debris rejection. A feasibility study of the adaptation of fringe scanning to ultra-high speed sorting (technically more difficult) will be made because of its potential for increased chromosomal resolution.